(406a) Operando Surface Enhanced Raman Spectroscopy Study of the Oxygen Reduction Reaction on a Non-Model Pt Catalyst

Hydrogen fuel cells are promising devices that can be utilized as a carbon neutral mobile energy source. The adoption of this technology has been hampered, however, by its poor technoeconomic performance, especially at scale¹. The high costs arise from the expensive platinum group metal catalysts needed to speed up the rate of the oxygen reduction reaction (ORR) at the fuel cell cathode. In recent years, efforts have been made to understand the mechanism of ORR at the elementary step level and at relevant reaction conditions^2,3. This has proven to be a difficult task as mechanistic analyses (in particular spectroscopic analysis of relevant surface intermediates) are confounded by solvent and electric field effects⁴. To shed light on the ORR mechanism, we have created a unique spectroscopic platform to probe the electrified Pt surface at realistic reaction conditions. A non-model Ag-Pt core-shell nanoparticle allows surface enhanced Raman spectroscopy (SERS) measurements to be conducted at the reactive and electrified Pt/electrolyte interface⁵. Experimental spectra are matched with density functional theory (DFT) derived vibrational modes to shed light on the reaction mechanics. The vibrational model assignments are further verified and validated by isotope labeling studies. Through this analysis, critical insights on the ORR mechanism are revealed that can be adopted as design criteria for future electrocatalyst optimizations.

1. Cano, Z. P. et al.Batteries and fuel cells for emerging electric vehicle markets. Nature Energy3, 279 (2018).
2. Kulkarni, A., Siahrostami, S., Patel, A. & Nørskov, J. K. Understanding Catalytic Activity Trends in the Oxygen Reduction Reaction. Chem. Rev.(2018).
3. Holewinski, A., Idrobo, J.-C. & Linic, S. High-performance Ag–Co alloy catalysts for electrochemical oxygen reduction. Nat. Chem.6, 828–834 (2014).
4. Holewinski, A. & Linic, S. Elementary Mechanisms in Electrocatalysis: Revisiting the ORR Tafel Slope. J. Electrochem. Soc.159, H864–H870 (2012).
5. Aslam, U. & Linic, S. Addressing Challenges and Scalability in the Synthesis of Thin Uniform Metal Shells on Large Metal Nanoparticle Cores: Case Study of Ag–Pt Core–Shell Nanocubes. ACS Appl. Mater. Interfaces9, 43127–43132 (2017).